Angle-dependence of strong-field ionization of singly- and doubly-charged carbonyl sulfide

We have studied the ionization probability of OCS molecules exposed to intense 780 nm laser pulses as a function of the angle between the molecular axis and the linear laser polarization. The molecules are exposed to two laser pulses. The first induces no ionization but, instead, creates a rotational wave packet within each molecule that exhibits preferential alignment in the laboratory frame at specific time delays. We measure the variation in the single and double ionization yield as a function of the delay between the two pulses. We obtain the angular dependent ionization probability by fitting the observed delay-dependent yield to moments of the angular distribution of the rotational wavepacket which can be accurately calculated. The experimentally determined angular distributions are compared to results of new time-dependent density functional theory predictions as well as previous measurements and calculations performed at somewhat lower laser intensities [1]. Accurate molecular ionization rate anisotropies are an important pre-requisite to utilizing strong-field techniques, such as high-harmonic spectroscopy, to probe of intramolecular electron dynamics. [1] J.L. Hansen et al., J. Phys. B 45, 015101 (2012); R. Johansen et al., J. Phys. B 49, 205601 (2016)